Method for protection of stone with fluorinated urethane

ABSTRACT

This invention relates to the application of fluorinated urethane compositions to stone in order to protect the stone from the deleterious effects of water and pollution.

FIELD OF THE INVENTION

This invention pertains to the application of fluorinated urethanecompositions to stone in order to protect the stone from the deleteriouseffects of water and pollution. Preservation of historic monuments,buildings, sculptures is one object of the present invention. Provisionof weather and pollution resistant stone construction materials isanother object of the present invention.

TECHNICAL BACKGROUND OF THE INVENTION

It has long been recognized that a combination of man-made and naturalatmospheric factors are having deleterious effects on stone structuresincluding many monuments of considerable artistic and historicalimportance. A variety of efforts have been undertaken over the years toidentify ways to protect and preserve these structures, but theseefforts have met with only partial success. Most recently, awell-organized and concerted effort has been undertaken by Piacenti andcoworkers, with sponsorship from the Target Project for the CulturalHeritage of the Consiglio Nazionale della Recerche of Rome, Italy, andrepresents the current state of the art.

Water, in the form of both rainfall and condensation, is the primarymaterial of concern, although organic matter may be of secondaryconcern. For example, all building materials are subject to stress andconcomitant cracking resulting from the penetration of water into thestructure of the material followed by cycles of freezing and thawing.Also, water in combination with CO₂, which occurs naturally, and nitrousand sulfurous gases, which are man-made pollutants, forms acids whichrapidly eat away at the stone.

A successful attack on the problem will necessitate some tradeoffs.While it is highly desirable to minimize the contact between water andstone, by achieving maximum water repellency, it is also necessary toprovide high water vapor permeability in order to permit venting of thatwater which finds its way into the microstructure of the stone.Substances with high permeability to water vapor are often not those ofthe highest water repellency. High resistance to acid and abrasion arealso of considerable importance. Furthermore, cost of materials is afactor in any practical application. The smaller the amount of materialrequired to achieve the desired effect, the better.

There are other tradeoffs. For example, it is particularly desirablethat the coating material coat but preferably not block the pores. Toachieve this, a coating must be applied with viscosity in a range whichpermits wetting of the pores via capillary action. High wetting is alsorequired to ensure thorough and uniform coverage. However, the coatingmust be provided with sufficient adhesion to the outside surface uponwhich it is deposited that at least some amount will remain thereon.

Other requirements for such materials include chemical inertness, lowvolatility, photooxidative stability, thermal stability, sufficientsolubility in environmentally friendly solvents to permit removal atsome future date. The coating must also be clear and colorless, andremain so for its lifetime. And it should be susceptible to dissolutionin environmentally friendly solvents for purposes of application. In thecurrent state of the art, the application solvent of choice issupercritical CO₂, as described in Carbonell et al., WO 99/19080.

In a series of patents, U.S. Pat. Nos. 4,499,146, 4,746,550, 4,745,009,4,902,538, Piacenti et al. disclose compositions based uponperfluoropolyethers having molecular weights in the range of 500-5000for use in the protection of stone from the effects of water andatmospheric pollutants. In the art of Piacenti, excellent combinationsof water repellency and water vapor permeability are achieved.

In U.S. Pat. No. 4,902,538, good results are achieved in compositionshaving highly crystalline particles of polytetrafluoroethylene andcopolymers thereof intermixed with the perfluoropolyethers. However,when stone of porosity of greater than ca. 30% is treated, impracticallyhigh levels of coating material are required to achieve the desiredcoverage with the desired water repellency. Levels in the range of atleast 150 g/m² are disclosed, more than 10 times the amount required forlow-porosity marble. The effect of this high coating level onpermeability is not disclosed. Its effect on cost, however, is clearlyundesirable. Furthermore, use of highly crystalline polymers, such aspolytetrafluoroethylene, is undesirable because, unless they aresintered at high temperatures, they will be too readily susceptible toremoval from the treated surface by abrasion and erosion. Further still,they are not readily soluble in the delivery medium of choice, CO₂, orany other desirable medium.

Also disclosed in the art in Piacenti et al., U.S. Pat. No. 4,764, 431,are copolymers of vinylidene fluoride which are less effective than theperfluoropolyethers.

Fluorinated acrylic polymers are disclosed by Ciardelli et al., Prog. inOrg. Coatings, 32, 43-50 (1997). The polymers disclosed therein arecharacterized by hydrocarbon backbones and fluorinated pendant groups.These polymers exhibit similar functionality to the perfluoropolyethers.

Guidetti et al. disclose the use of polyfluorourethanes for protectingstone in “Polyfluorourethanes as stone protectives”, 7th InternationalCongress on Deterioration and Conservation of Stone, 1053-62 (1992).

There is considerable incentive in the art to discover new materialswhich possess several of the above attributes desired for theapplication.

SUMMARY OF THE INVENTION

The present invention provides a process for protecting stone comprisingcontacting stone with a non-polymeric composition having the formula

(R²O₂CNH)_(p)R¹NHCO—(OCHR³CH₂)_(m)—X_(n)—R_(f)

where p=1 or 2, R¹ is an aliphatic, cycloaliphatic or aromatichydrocarbyl di- or tri-radical, R² is a fluorinated or non-fluorinatedhydrocarbyl or hydroxy-hydrocarbyl radical optionally substituted by oneor more ether oxygens, R³ is hydrogen or alkyl, X is a diradicalselected from the group consisting of —OCH₂CH₂—, —OCH₂CH₂N(R⁴)SO₂—,—CH₂—, —O—, and —OCH₂—, wherein R⁴ is alkyl, R_(f) is perfluoroalkyl,and m=0-30, n=0 or 1, with the proviso that if n=0 or if n=1 and X is—O—, then m≠0.

DETAILED DESCRIPTION

For the purpose of the present invention, the term “stone” means anatural stone used in construction or sculpture (such as granite,marble, limestone, or sandstone) as well as tile, cement, brick, stucco,and the like.

The method of the present invention provides surprising benefits overthe methods of the art. In the method of the present invention, aslightly fluorinated non-polymeric urethane composition is employed as acoating agent for stone in order to provide high liquid moisturebarrier, good moisture vapor permeability, and resistance toenvironmental pollutants. The non-fugitive, very low areal densitycoating formed on the stone surface is surprisingly effective over thematerials of the art. Furthermore, the urethane of the present inventionis readily soluble in a variety of solvents by virtue of itsnon-polymeric nature, and is thereby both readily applied in the form ofan environmentally friendly solution and readily removed by conventionalsolvents should that be deemed necessary after application. Furtherstill, the highly desirable effects of the method of the presentinvention are achieved employing a urethane containing relatively littleof expensive fluorocarbon ingredients.

Suitable for the practice of the present invention are urethanesrepresented by the formula

(R²O₂CNH)_(p)R¹NHCO—(OCHR³CH₂)_(m)—X_(n)—R_(f)

where p=1 or 2, preferably p=1. R¹ is an aliphatic, cycloaliphatic oraromatic hydrocarbyl di- or tri-radical. Preferably R¹ is a di-radical;more preferably, R¹ is a cycloaliphatic diradical. R² is a fluorinatedor non-fluorinated hydrocarbyl or hydroxyhydrocarbyl radical optionallysubstituted by one or more ether oxygens. Preferably the urethanes are amixture where R² is R_(f) and/or alkyl. Most preferably R² is R_(f)and/or methyl or ethyl. R³ is hydrogen or alkyl, preferably R³ ishydrogen. X is a diradical selected from the group consisting of—OCH₂CH₂—, —OCH₂CH₂N(R⁴)SO₂—, —CH₂—, —O—, and —OCH₂—, wherein R⁴ isalkyl. R_(f) is a perfluoroalkyl radical, and may in practice be amixture of perfluoroalkyl radicals, m=0-30, n=0 or 1, with the provisothat if n=0 or if n=1 when X is —O—, then m≠0. Preferably, n=0, and m=1to 20, most preferably m=1.

In a preferred embodiment, R¹ is a cycloaliphatic diradical representedby the formula

wherein and R⁵, R⁶, and R⁷ are all alkyl, preferably methyl.

The urethanes suitable for use in the present invention are known in theart and may be synthesized according to the methods described in Antonet al., U.S. Pat. No. 5,859,126, Anton, U.S. Pat. No. 5,637,657, andAnton et al., U.S. Pat. No. 5,605,956.

In a preferred embodiment, the fluorinated organic urethane is an adductof a fluorinated monofunctional alcohol, a non-fluorinated organicpolyisocyanate and a non-fluorinated organic alcohol. Suitablepolyisocyanates include aromatic, aliphatic and cycloaliphatic di andtrifunctional polyisocyanates such as 1,6-hexamethylene diisocyanate,isophorone diisocyanate, 4,4′-biphenylene diisocyanate, toluenediisocyanate, bis cyclohexyl diisocyanate, tetramethylene xylenediisocyanate, ethyl ethylene diisocyanate, 2,3-dimethyl ethylenediisocyanate, 1-methyltrimethylene diisocyanate, 1,3-cyclopentylenediisocyanate, 1,4-cyclohexylene diisocyanate, 1,3-phenylenediisocyanate, 1,5-naphthalene diisocyanate,bis-(4-isocyanatocyclohexyl)-methane diisocyanate,4,4′-diisocyanatodiphenylether diisocyanate and the like.

Typical trifunctional isocyanates that can be used are triphenylmethanetriisocyanate, 1,3,5-benzene triisocyanate, 2,4,5-toluene triisocyanateand the like. Oligomers of diisocyanates also can be used such as thetrimer of hexamethylene diisocyanate which is sold under the tradename“Desmodur” N. Preferably, aliphatic diisocyanates would be used and mostpreferably cycloaliphatic diisocyanates.

Preferred fluorinated monofunctional alcohols are represented by theformula

R_(f)—(X)_(n)—(CH₂CHR³—O)_(m)—H

where R_(f) is preferably a straight chain or branched chain fluoroalkylor chlorofluoroalkyl group having 4-20 carbon atoms optionallysubstituted by ether oxygen. Preferably, R_(f) is a perfluoroalkyl grouphaving 4-20 carbon atoms and most preferably, R_(f) is a perfluoroalkylgroup containing 6-12 carbon atoms. X is a divalent radical, preferably—CH₂CH₂O—, —SO₂N(R⁴)CH₂CH₂O—, —CH₂—, —O—, or —CH₂O— where R⁴ is an alkylgroup preferably having 1-4 carbon atoms. R³ is H or an alkyl grouphaving 1-4 carbon atoms, H and methyl being preferred. n is 0 or 1 and mis 0-30, provided that if n is 0 or if n=1 and X is —O—, then m must begreater than or equal to 1; preferably n=0 and m is 1 to 20. Mostpreferably, m=1.

Preferred fluorinated monofunctional alcohols are represented by one ofthe following formulae:

R_(f)—(CH₂CH₂—O)_(m)H

where R_(f) is a perfluoroalkyl group having 6 to 12 carbon atomsoptionally substituted by ether oxygen and m is 5 to 15;

H—(CF₂CF₂)_(m)—CH₂OH

where m is 1-6;

C₈F₁₇—SO₂—N(R⁵)—(CH₂CH₂O)_(m)—H

where R⁵ is an alkyl group having 1-4 carbon atoms and m is 1-30,preferably m is 1-20;

CF₃—(O—C(CF₃)(F)CF₂)_(p)—O—(CH₂CH₂O)_(m)—H

where n is 0-10 and m is 1-20; and

R_(f)—CH₂CH₂—OH

where R_(f) is described above.

A number of fluorinated alcohols are available commercially as Zonyl®Fluorotelomer Intermediates from E.I. du Pont de Nemours and Company,Wilmington, Del.

Other perfluoroalkyl alcohols can also be used in the present invention,such as 2-N-methyl-N-ethanolperfluorooctane sulfonamide, availablecommercially from Dainippon Ink and Chemical, Inc., Tokyo 103, Japan.Fluorinated diols prepared by the procedure of U.S. Pat. No. 4,946,992and fluorinated thiols prepared as in U.S. Pat. No. 3,544,663, inparticular Example 1 therein, are also suitable.

It will be understood by the practitioner of the art that theingredients employed in the reaction to form the urethane of the presentinvention, and therefore the product urethane generated therefrom may bemixtures of one or more of the compounds hereinabove said to be suitablefor the practice of the invention. In particular, the Zonyl®Fluorotelomer Intermediates preferred are in fact mixtures of ahomologous series of species represented by the formula

CF₃(CF₂CF₂)_(n)CH₂CH₂OH

where n is 3 to 9.

The fluorinated organic urethane of the method of the present inventionis prepared as taught in the art hereinabove cited, in which thefluorinated monofunctional alcohol, organic polyisocyanate and organicalcohol are charged into a reaction vessel optionally with solvents anda catalyst for about 0.1-4 hours and heated to about 50°-120° C.,preferably 60°-85° C.

About 0.1 to 100 mole % of active isocyanates are reacted with thefluorinated alcohol. Preferably, greater than 40% of the isocyanates arereacted with the fluorinated alcohol and most preferably greater than75%. The remaining isocyanates are reacted with monofunctional organicalcohols such as allyl or propyl alcohols.

Typical solvents that are used are alkyl acetates such as ethyl acetate,butyl acetate and the like, alkylene glycol alkyl ether acetates such asethylene glycol, monobutyl ether acetate and the like and ketones suchas acetone, methyl ethyl ketone, and methyl isobutyl ketone.

Typical catalysts that are used are organo tin containing catalysts likealkyl tin laurates such as di-n-butyl tin dilaurate, dibutyl tindi-2-ethylhexoate, stannous octoate, stannous oleate and the like.

In the practice of the present invention, one or more of the urethaneshereinabove described are applied by any convenient method to thesurface of the stone which is to be protected from the effects of water,such as rainfall, and environmental pollutants. Foremost, the coatingmust provide a barrier to liquid water with minimal effect on thenatural water vapor permeability of the stone. One way of achieving thisis to provide durable coating in as thin a layer as possible on the wallsurface of each pore of the stone without actually filling or blockingthe pore using a material of the lowest possible surface tension.Coating materials which exhibit a desirable combination of propertiesare characterized by pendant groups comprising perfluoralkyl functionalgroups in sufficient concentration that the surface presented toincident liquid water such as rainfall is characterized by a highdensity of the perfluorinated groups and a consequently very low surfacetension. In the most preferred embodiment of the urethane of the methodof the present invention, the perfluoralkyl group in R_(f) ashereinabove defined has at least 7 carbons in a linear chain. Theresulting low surface tension achieved by the application of thepreferred urethane to a porous stone surface is the source of thethermodynamic driving force for complete wetting of the pores as well asliquid water repellency. To reduce the kinetic barrier to complete porewetting, the viscosity should be as low as possible. This represents aparticularly desirable attribute of the method of the present inventionbecause the urethane employed in the method of the present invention isa non-polymeric liquid which readily forms low viscosity solutions in anumber of convenient solvents.

While in no way limiting the scope of the invention, it is estimatedthat the viscosity of the coating during application of the coating tothe stone is preferably less than about 10 Pa-s to achieve optimumcoating performance. It will be obvious to one of skill in the art thatwhile it is desirable to employ materials which afford low viscositysolutions, usually associated with low molecular weight or non-polymericmaterials, the materials so employed cannot be of such low molecularweight that they evaporate from the stone surface. Until the discoveryof the method of the present invention, all materials in the artemployed for application to stone for the purpose of preservation havebeen polymeric.

It is further preferred that polar groups such as urethanes should bepresent in the coating material to promote adhesion of the coatingmaterial to the stone surface and decrease the tendency of the coatingmaterial to continually penetrate to the interior of the stone andreducing surface efficacy in terms of liquid water repellency. Esters,amides, and —CH₂CF₂— moieties are examples of other suchadhesion-promoting polar groups.

While according to the method of the present invention it is possible toapply the urethane to the stone in neat chemical form, using methodssuch as are known in the art such as painting or spraying, it ispreferred to dissolve the urethane in a solvent which acts as a volatilediluent in the spraying operation to afford fast penetration at theearly stages of coating while providing a high degree of control overthe viscosity, the uniformity of coating and the coating thickness.

Solvents suitable for the practice of the present invention includeacetone, methyl-ethyl ketone, ethyl acetate, t-butyl acetate, methylisobutyl ketone (MIBK), hydrochlorofluorocarbons, perfluorocarbons. Inthe most preferred embodiment, the urethane of the present invention isdissolved in supercritical CO₂ according to the methods described inCarbonell et al., WO 99/19080 or in the alternative in U.S. Pat. Nos.4,923,720; 5,108,799; 5,290,603; and 5,290,604. Methyl isobutyl ketoneis a preferred solvent for malting the urethanes as well as for dilutingit to a suitable viscosity for absorption into stone within a practicaltime period. A preferred concentration of MIBK is urethane is 10% to 20%by weight.

These materials would preferably be sprayed from CO₂ solutions of 75weight % or less polymer at 40 to 70° C., 2000 to 4000 psi. To promotematerial absorption into the stone it might also be preferable to add upto about 40 weight % acetone, t-butyl acetate, Oxol 100(4-chlorobenzotrifluoride), or other such environmentally friendlydiluent to the urethane.

It will be understood by one of skill in the art that numerous chemicalcompounds have been identified which may serve as the supercriticalfluid for the urethane coating composition of the invention. However,CO₂ is by far the preferred compound because of the low cost, lowtoxicity, ready formation of a supercritical fluid, and lowenvironmental impact.

The urethane component of the coating composition is generally presentin amounts ranging from 1 to 80 weight percent, based upon the totalweight of the coating composition. Preferably, the urethane componentshould be present in amounts ranging from about 15 to about 55 weightpercent on the same basis.

The supercritical fluid diluent should be present in such amounts that aliquid mixture is formed that possesses such a viscosity that it may beapplied as a liquid spray. Generally, this requires the mixture to havea viscosity of less than about 300 centipoise at spray temperature.Preferably, the viscosity of the mixture of components ranges from about5 centipoise to about 150 centipoise. Most preferably, the viscosity ofthe mixture of components ranges from about 10 centipoise to about 50centipoise.

The supercritical carbon dioxide fluid is most preferably present inamounts ranging from about 45 to about 85 weight percent on the totalcompositional weight, thereby producing a mixture having viscositiesfrom about 10 centipoise to about 50 centipoise at spray temperature.

While the art of applying coatings from supercritical CO₂ teaches theuse of an organic solvent in combination with a polymeric coatingmaterial and supercritical CO₂, it is a particularly useful aspect ofthe present invention that the preferred urethane composition of theinvention is a liquid at room temperature, and it is not necessary toform a low-viscosity solution or dispersion for mixing with the CO₂. Itis however optional to add a third component to the coating compositionof the invention, the third component comprising one or more organicsolvents employed for the purpose of improving viscosity control duringspraying and “laydown” of the coating material on the stone.

The organic solvents suitable for the practice of the most preferredembodiment of the invention generally include any solvent or mixture ofsolvents that is miscible with CO₂, is a good solvent for the urethane,and is fugitive at the temperature at which the coating is being appliedto the stone, normally at temperatures of about 0° C. or above.Preferably, the solvent is also environmentally friendly. Suitableorganic solvents include acetone, methyl-ethyl ketone, methyl isobutylketone, ethyl acetate, t-butyl acetate, hydrochlorofluorocarbons, andperfluorocarbons with acetone, methyl-ethyl ketone, ethyl acetate andt-butyl acetate preferred.

The coating composition of the invention is sprayed onto a substrate toform a liquid coating thereon by passing the liquid mixture underpressure through an orifice into the environment of the substrate toform a liquid spray.

Spray orifices, spray tips, spray nozzles, and spray guns used forconventional airless and air-assisted airless spraying of coatingformulations such as paints, lacquers, enamels, and varnishes, aresuitable for spraying the coating composition of the present invention.The spray pressure used in the practice of the present invention is afunction of the specific coating formulation. In the case ofsupercritical fluid solutions, the minimum spray pressure is at orslightly below the critical pressure of the supercritical fluid.Generally the pressure will be below 5000 psi. Preferably, the spraypressure is above the critical pressure of the supercritical fluid andbelow 3000 psi. If the supercritical fluid is supercritical carbondioxide fluid, the preferred spray pressure is between 1070 psi and 3000psi. The most preferred spray pressure is between 1200 psi and 2500 psi.

The spray temperature used in the practice of the present invention is afunction of the coating formulation. The minimum spray temperature isabout 31° C. The maximum temperature is determined by the thermalstability of the components in the liquid mixture. The preferred spraytemperature is between 35° C. and 90° C. The most preferred temperatureis between 45° C. and 75° C. Generally liquid mixtures with greateramounts of supercritical carbon dioxide fluid require higher spraytemperatures.

One of skill in the art will recognize that the method of the presentprocess, while specifically directed to the protection of stone, mayequally be employed to apply coatings to a variety of substrates.Examples of suitable substrates include but are not limited to metal,wood, glass, plastic, paper, cloth, ceramic, masonry, stone, cement,asphalt, rubber, and composite materials.

Through the practice of the present invention, coatings may be appliedto substrates in thicknesses of from about 0.5 to 100 micrometers.Preferably, the coatings have thicknesses of from about 1.0 to about 15micrometers, while most preferably, their thicknesses range from about1.5 to about 10 micrometers.

The method of the present invention provides a considerable benefit inthat the urethane coating may be readily removed using inexpensive andenvironmentally benign solvents such as t-butyl acetate and acetone ifit should be deemed desirable at some point in time following theapplication thereof.

The coatings on stone produced by the practice of the present inventionare highly beneficial to the purpose of protecting the stone fromenvironmental degradation. Two key attributes which are indicative ofsusceptibility to weathering are water absorption, typically bycapillary action through the porous stone structure, and water vaporpermeation rate. It is highly desirable that the water absorption ofnormally highly absorbent stone be reduced by as large a factor aspossible, while water vapor permeability, normally high as well, bemaintained at a high level. The coated stone of the present inventionprovides both high levels of water vapor permeability by virtue of thethin coatings which are found to be effective in providing the desiredhigh resistance to water penetration.

The method of the present invention and the properties of the coatedstone compositions provided thereby are further illustrated in thefollowing specific embodiments.

EXAMPLES

In the following examples, a pressure cell as described in Tuminello etal., J. Appl. Polym. Sci., 56, 495 (1995)., was used to evaluate thesolubility of the urethane specimens below in CO₂. The total volume ofthe cell was about 3.0 ml. Solid fluorinated material solute sufficientto make about a 17 volume percent solution was added to the cell first.A vacuum was applied for a few minutes and then liquid CO₂ was addeduntil the cell was filled at its vapor pressure, about 6.2 MPa (900psi). Pressures could be increased to as high as 31.7 MPa (4600 psi) bypushing a piston through a manifold loaded with CO₂. Temperature wasincreased to as high as 100° C. with an electrical heating band aroundthe pressure chamber. Temperatures as low as about −10° C. were achievedby removing the heating band and packing dry ice around the cell. Cloudpoint was determined by visual observation through the sapphire windowsprovided on the cell. Cloud point was determined at constant temperaturewith decreasing pressure and is defined as that pressure at which themixture became so opaque that it was no longer possible to see thestirring paddle inside the cell. Cloud point data for each sample islisted below.

In the following examples, the procedures followed in determining waterabsorption and permability were essentially those described in Italianstandard test methods AA.VV, Assorbimento di acqua per capillarità,Raccomandazione NORMAL 11/85, CNR-ICR, Roma 1985 and 7 AA.VV,Permeabilità al vapor d'acqua, Raccomandazione NORMAL 121/85, CNR-ICR,Roma 1985.

Two stone substrates were employed, each in the form of prism-shapedspecimens 5×5×2 cm in size. They were:

(a) Marble—White Carrara marble with grey veins, 99% calcite, polygonalstructure and fine grains. Total porosity=3.83±0.2%; saturationindex=7.4±0.6%.

(b) Biocalcarenite—Lecce stone composed of Foraminifera with calcareousshell, glauconite grains and very small fragments of quartz. The clastsare bound by a micritic calcitic cement with a low clay content. Totalporosity=32 to 40%; saturation index=65±5.0%.

In each example, the average of the results obtained on three separateprism shaped specimens was determined. Five untreated stone specimens ofeach type were retained as controls. The stone specimens were maintainedin a dessicator containing CaCl₂ until a constant mass was reached usinga lab balance of precision of ±1 mg.

The coating was applied (from 2 weight % reagent grade acetonesolutions) to one face of each stone specimen by painting with a brushas uniformly as possible. This was done after removing the stone fromthe dessicator. Coating thickness was determined by weighing before andafter treatment. The painted stone specimens were then left at roomtemperature in ambient air for one week to evaporate the solvent andthen placed in a dessicator along with the control specimens containingCaCl₂ until constant mass was achieved.

Each stone specimen thus brought to constant mass, was removed in turnfrom the dessicator and placed in contact with a stack of filter paper(1 cm thick; 9 cm diameter) soaked in distilled water. The amount ofwater absorbed by capillarity was determined by weighing the sampleafter a fixed time (marble—60 min.; biocalcarenite—20 min). Protectiveefficacy (E_(p)%) was calculated by the following expression:${E_{P}\%} = {\frac{\left( {A_{UN} - A_{T}} \right)}{A_{UN}} \cdot 100}$

where A_(UN) and A_(T) are the amounts of water absorbed by theuntreated and treated samples, respectively.

In the ideal there would be no water absorption, or E_(p)%=100. In thecurrent state of the art, a very good level of efficacy is considered tobe 80 to 90%.

Each stone test specimen was mounted as a lid to a poly(vinyl chloride)test cell containing 10 ml of distilled water. The cell was equippedwith neoprene gaskets to keep the sample in place while leaving an areaof about 16 cm² through which water vapor could permeate. The cell wasthen placed in a thermostatic drybox maintained at a constanttemperature of 25.0±0.5° C., and containing a sufficient amount ofsilica gel and calcium chloride to maintain constant relative humidityof 2 to 5%.

A balance was placed in the drybox to monitor weight changes in the cellwithout the need to open the drybox. The weight of each cell wasmonitored every 24 hours for several days. Weight loss became constantafter a few days. The permeability (P) of the surface of the stone towater vapor was calculated using:

P=M/A(g/m ² in 24 hrs.)

where M is the amount of water, in grams, lost in 24 hours and A is theevaporating area, in m², of the system.

The reduction in permeability (R_(p)%) due to the treatment is definedas:${R_{P}\%} = {\frac{\left( {P_{UN} - P_{T}} \right)}{P_{UN}} \cdot 100}$

where P_(UN) and P_(T) are the permeability of the untreated and treatedsamples, respectively. This procedure is described in more detailelsewhere. The best performance is to have permeability matching that ofthe untreated sample, or R_(p)%=0.

Examples 1 and 2 IPDI/TBA/ROH (50:50)

Isophorone diisocyanate was reacted with telomer B alcohol,CF₃(CF₂)₄₋₁₂CH₂CH₂OH, in a mole ratio of 1:1 so that 50% of theisocyanates reacted to form a fluorinated urethane. The reaction wasthen finished by reacting the remaining isocyanate moieties with allylalcohol to produce a mixture of fluorinated urethanes representedprimarily by the structures:

It is estimated that the mixture contained less than 3% each of thediisocyante ring having both cyanate groups reacted with either thetelomer B alcohol or the allyl content was 41.5% by weight.

Solubility of the mixture so produced was determined by cloud pointobservations as described hereinabove. The results, shown, in Table 1,indicate a high degree of solubility in super critical CO₂.

TABLE 1 Cloud Point in Supercritical CO₂ Temperature (° C.) Cloud Point(psi) 25 1170 26 1130 30 1413 33 1510 35 1642 39 1770 41 1879 44 2017 452015 49 2218 52 2290 53 2424 55 2476 59 2615 60 2665 63 2700 65 2812 692975 70 3028 74 3130 75 3263

2 g of the mixture so prepared was dissolved in 98 g of acetone at roomtemperature. The resulting solution was applied to three stone specimenseach of the white Cararra marble (Example 1) and Lecce stone (Example2), as hereinabove described. The specimens were allowed to stand for 1week, after which they were subject to the procedures of dessication,water absorption determination, and water vapor permeability accordingthe methods hereinabove described. Results are shown in Table 3.

Examples 3 and 4 IPDI/TBA/ROH (95:5); Designation TLF-9158

Isophorone diisocyanate (IPDI) was reacted with telomer B alcohol (TBA)as in Example 1 except that the mole ratio was ca. 2:1 TBA:IPDI so thatabout 95% of the isocyanates reacted with TBA. The reaction was drivento completion by reacting the remaining isocyanate with propyl alcohol.The resulting urethane was a mixture of ca. 90 mol-% of the diurethanerepresented by the structure:

and approximately 10 mol-% of a mixture of the two chemical structuresof Example 1 wherein the allyl moiety is replaced by a propyl moiety.The fluorine content of the urethane so produced was 50.9%.

Solubility of the mixture so produced was determined by cloud pointobservations as described hereinabove. The results, shown, in Table 2,indicate a high degree of solubility in super critical CO₂.

TABLE 2 Solubility in Supercritical CO₂ Temperature (° C.) Cloud Point(psi) 28 1057 30 1260 35 1396 41 1680 43 1833 46 1894 51 2146 56 2307 582458 60 2460 64 2602 70 2892

The procedures of Example 1 were followed to prepare and test stonespecimens. Example 3 was the marble, and Example 4, the Lecce stone. Theresults are shown in Table 3.

Comparative Example 1 CF₃—[CF(CF₃)CF₂O]_(m)—(CF₂O)_(n)—CF₃

The test procedures of Example 1 were followed employing Fomblin® YR, aperfluorinated polyether available from Ausimont/Montefluos,Montedison/Montefluos Group, Milano, Italy. Fomblin® YR is the materialcurrently preferred in commercial stone preservation applications. Stonetest specimens were prepared and tested as hereinabove described. Onlythe biocalcarenite was tested. The amount of material applied was thatfollowed in current commercial practice. Results are in Table 3.

TABLE 3 Results of Coating on Stone Protective Reduction in CoverageEfficacy Permeability Example Substrate (g/sq.m.) (Ep %)* (Rp %)** 1Marble 3.3 ± 0.3 67 ± 7 33 2 Biocalcarenite 12.1 ± 0.8  65 ± 1 19 3Marble  3.1 ± 0.11 86 ± 1 28 4 Biocalcarenite 7.4 ± 0.7 75 ± 2 10 Comp.Ex. 1 Biocalcarenite 49 18 Not Determined Control Marble None  0  0Control Biocalcarenite None  0  0 *Goal is 100% **Goal is 0%

Comparative Example 2

Following the method described in F. Piacenti and M. Camaiti, J.Fluorine Chem., 69 (1994), 227-235, the monofunctional acid fluorideprecursor of a random perfluoropolyether of similar structure to the onein Comparative Example 1 was esterified and then condensed withhexamethylene diamine to form the diamide functionalizedperfluoropolyether material with a MW of about 1800 Da. This material isconsidered the state of the art for providing a combination of highwater repellency and low water permeability, as described in F.Piacenti, “The Conservation of Monumental Buildings: Recent ScientificDevelopments”, a lecture presented at the 2^(nd) International Congresson Science and Technology for the Safeguard of Cultural Heritage in theMediterranean Basin—Paris—Jul. 5 to 9, 1999.

Biocalcarenite specimens were coated with 48 g/m² of theperfluoropolyether diamide so prepared according to the methods ofComparative Example 1. E_(p) was 55% as determined as hereinabovedescribed.

What is claimed is:
 1. A process comprising contacting stone with anon-polymeric urethane having the formula(R²O₂CNH)_(p)R¹NHCO—(OCHR³CH₂)_(m)—X_(n)—R_(f) wherein p=1 or 2, R¹ isan aliphatic, cycloaliphatic or aromatic hydrocarbyl di- or tri-radical,R² is a fluorinated or non-fluorinated hydrocarbyl or hydroxyhydrocarbylradical optionally substituted by one or more ether oxygens, R³ ishydrogen or alkyl, X is a diradical selected from the group consistingof —OCH₂CH₂—, —OCH₂CH₂N(R⁴)SO₂—, —CH₂—, —O—, and —OCH₂—, wherein R⁴ isalkyl, R_(f) is perfluoroalkyl, and m=0-30, n=0 or 1, with the provisothat if n=0, or if , n=1 and X is —O—, then m≠0 and wherein the processfurther comprises forming a solution of said non-polymeric urethaneprior to contacting said stone therewith, wherein said stone iscontacted with said solution of said non-polymeric urethane.
 2. Theprocess of claim 1 wherein p=1, R¹ is a diradical, R² is perfluoroalkylor alkyl.
 3. The process of claim 2 wherein R¹ is a cycloaliphaticdiradical, R² is methyl, ethyl, or perfluoroalkyl, R³ is hydrogen, n=0,and m=1 to
 20. 4. The process of claim 3 wherein m=1, R² is aperfluoroalkyl radical having from 5-13 carbons, and R¹ is acycloaliphatic diradical represented by the formula

wherein R⁵, R⁶, and R⁷ are all methyl.
 5. The process of claim 4 whereinR⁵, R⁶, and R⁷ are methyl.
 6. The process of claim 1 wherein saidsolution comprises supercritical CO₂.
 7. The process of claim 6 whereinsaid solution further comprises an organic solvent which is fugitive ata temperature at or above about 0° C.
 8. The process of claim 7 whereinsaid organic solvent is selected from the group consisting of acetone,methyl-ethyl ketone, methyl isobutyl ketone, ethyl acetate, t-butylacetate, hydrochlorofluorocarbons, and perfluorocarbons.
 9. The processof claim 7 wherein the solvent is methyl isobutyl ketone.
 10. Acomposition comprising stone and a non-polymer urethane having theformula (R²O₂CNH)_(p)R¹NHCO—(OCHR³CH₂)_(m)—X_(n)—R_(f) wherein p=1 or 2,R¹ is an aliphatic, cycloaliphatic or aromatic hydrocarbyl di- ortri-radical, R² is a fluorinated or non-fluorinated hydrocarbyl orhydroxyhydrocarbyl radical optionally substituted by one or more etheroxygens, R³ is hydrogen or alkyl, X is a diradical selected from thegroup consisting of —OCH₂CH₂—, —OCH₂CH₂N(R⁴)SO₂—, —CH₂—, and —OCH₂—,wherein R⁴ is alkyl, R_(f) is perfluoroalkyl, and m=0-30, n=0 or 1, withthe proviso that if n=0, or if n=1 and X is —O—, then m≠0, and whereinsaid non-polymeric urethane is in the form of a coating on said stoneand wherein said coating has a thickness in the range of 1.5 to 10micrometers.
 11. The composition of claim 10 wherein p=1, R¹ is adiradical, R² is perfluoroalkyl or alkyl.
 12. The composition of claim11 wherein R¹ is a cycloaliphatic diradical, R² is methyl, ethyl, orperfluoroalkyl, R³ is hydrogen, n=0, and m=1 to
 20. 13. The compositionposition of claim 12 wherein m=1, R²is a perfluoroalkyl radical havingfrom 5-13 carbons, and R₁ is a cycloaliphatic diradical represented bythe formula

wherein R⁵, R⁶, and R⁷ are all alkyl.
 14. The composition of claim 13wherein R⁵, R⁶, and R⁷ are methyl.